Heavy work vehicles used in the building sector are known, usually consisting of a truck on which an arm is assembled which has a plurality of articulated segments pivoted with respect to each other at the ends. The arm can be oriented, extended and/or telescopically opened for the distribution of concrete or similar material. The arm is able to reach considerable distances from the truck so as to guarantee maximum flexibility of use of the heavy work vehicle. The overall weight of the arm increases with the increase in distance which it can reach, and this depends on the number and the length of the articulated segments which make it up. The need for flexibility therefore conflicts with the limits of bulk and weight of the arm itself.
From the European patent application EP-08164624.2, in the name of the present Applicant, an extendable arm is known for the distribution of concrete, at least partly made of composite material so as to reduce the weight of the arm, given the same extension reached, with respect to a traditional arm made of metal material. The composite material has good characteristics of resistance and rigidness, but also greater lightness.
Based on the idea of using composite material for the construction of the articulated arm, the European patent application EP-08152672.5, also in the name of the present Applicant, shows a possible construction technique for the arm, which aims to reduce production costs, guaranteeing maximum flexibility and versatility of production. According to this technique each main box-like structure of the segments of the arm is formed by depositing a predefined plurality of layers of pre-impregnated composite material in a forming mold. Then this box-like structure made of composite material is subjected to polymerization and, once removed from the mold, terminal joint elements are attached to it in order to attach it to other adjacent segments, in order to form, once assembly is completed, an arm with articulated segments. At the same time as the arms were designed, an experiment was made with a gluing technique to glue the box-like structure to a joint element so as to form a complete segment. More specifically, in FIG. 4 a gluing area 122 between ends 123a and 124a is schematically shown, belonging respectively to a box-like structure 123 and to a joint element 124 of a generic articulated segment 112-116. The ends 124a of the element 124 are coupled parallel and glued on the outside to the respective ends 123a of the structure 123 by means of a layer of glue, or other adhesive material 25 interposed. The angle formed between the longitudinal axis of the box-like structure 123 and the profile of the end 123a of the box-like structure 123 is zero. Experimental tests showed that, during the action of the arm, on the layer of glue 25 a shearing power is exerted coincident with the axial force generated by a flexion moment applied. The axial force is parallel to the longitudinal axis of the articulated segment 112-116 considered. It was shown experimentally that the tension state, and therefore the resistance criterion for the layer of glue 25, is dominated, for the most part, by the action of the shearing force, defined as that force which tends to make the overlapping ends 123a and 124a slide one on top of the other.
One disadvantage of this gluing method is that the layer of glue 25 is in a high state of tension when the articulated segment 112-116 is in use. Indeed the shearing force is high, coinciding with the axial force applied. Consequently, the stresses which affect the layer of glue interposed between the boxed beams and the terminal joint are high, and the fatigue damage is significant, resulting in a limited working life of the articulated segment and therefore of the arm which it comprises.
Purpose of the present invention is to make an element, or segment, of an articulated arm in which the technique of connecting the boxed beam and terminal joint allows to lengthen the duration of the working life of the arm.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.